A new method of detecting interferogram in differential phase-contrast imaging system based on special structured x-ray scintillator screen

An x-ray scintillator screen with a special structure, functioning as detector and analyser grating, was proposed for collecting the interferogram of differential phase contrast imaging without absorption grating and difficulty of fabrication by a state of the art technique. On the basis of phase grating diffraction, a detecting model of the scintillator screen was built for analysing the phase and absorption information of objects. According to the analysis, a new method of phase retrievals based on two-images and the optimal structure of screen were presented.

Development of x-ray scintillator functioning also as an analyser grating used in grating-based x-ray differential phase contrast imaging

In order to push the grating-based phase contrast imaging system to be used in hospitM and laboratories, this paper designs and develops a novel structure of x-ray scintillator functioning also as an analyser grating, which has been proposed for grating-based x-ray differential phase contrast imaging. According to this design, the scintillator should have a periodical structure in one dimension with the pitch equaling the period of self-image of the phase grating at the Talbot distance, where one half of the pitch is pixellated and is made of x-ray sensitive fluorescent material, such as CsI（T1）, and the remaining part of the pitch is made of x-ray insensitive material, such as silicon. To realize the design, a deep pore array with a high aspect ratio and specially designed grating pattern are successfully manufactured on 5 inch silicon wafer by the photo-assisted electrochemical etching method. The related other problems, such as oxidation-caused geometrical distortion, the filling of CsI（T1） into deep pores and the removal of inside bubbles, have been overcome. Its pixel size, depth and grating pitch are 3 p.m^7.5 ~m, 150 p^m and 3 Ixm, respectively. The microstructure of the scintillator has been examined microscopically and macroscopically by scanning electron microscope and x-ray resolution chart testing, respectively. The preliminary measurements have shown that the proposed scintillator, also functioning as an analyser grating, has been successfully designed and developed.

Performance evaluation of CsI screens for X-ray imaging

CsI film has been one of the most extensively used scintillators for indirect X-ray imaging because of its needle-like micro-structure. The purpose of this paper is to investigate the imaging performance of CsI screen as a function of thickness and radiation quality. Four multilayer scintillation screens with microcolumnar CsI：T1 film （thicknesses of 50 μm, 100 μm, 200μm and 300 μm） included were prepared and coupled to an optical imaging sensor. The modulation transfer function （MTF）, normalized noise power spectrum （NNPS） and detective quantum efficiency （DQE） of these screens were evaluated based on the standard IEC 62220-1, and the results indicated that, in the medium spatial frequency range （1-6 lp/mm）, the MTF of CsI screens with the same thickness was lower when the incident X-ray photon energy was higher, possibly owing to scattering and K-fluorescence re-absorption effects. The NNPS in the higher spatial frequency range （above 8 lp/mm） is dominated by stochastic noise while the entrance surface air Kerma （ESAK） decreases. For 100 μm, 200 μm and 300 μm thick CsI screens, the DQE under RQA7 and RQA9 is lower than that under RQA3 and RQA5 due to low absorption efficiency.

Performance assessment of Cs I(T1) screens on various substrates for X-ray imaging

Thallium-doped cesium iodide（Cs I（Tl）） screens are widely used in X-ray imaging devices because of the columnar structure of the Cs I（Tl） layer, but few reports focus on the optical role of the substrate in the screen system.In this paper, four substrates including fused silica（Si O2）, silver-film coated Si O2, graphite（C） and fiber optic plate（FOP） are used to fabricate Cs I（Tl） screens by thermal evaporation. Their imaging performance is evaluated by relative light output（RLO）, modulation transfer function（MTF）, normalized noise power spectrum（NNPS） and noise equivalent quanta（NEQ）. The results reveal that although Cs I（Tl） film on graphite plate yields images with the lowest light output, it presents relatively higher spatial resolution and better signal-to-noise characteristics.However, films on Si O2 plate obtain low MTF but high NNPS curves, whether they are coated with silver film or not.Furthermore, scintillation screens on FOP have bright images with low NNPS and high NEQ, but have the lowest MTF. By controlling the substrate optical features, Cs I（Tl） films can be tailored to suit a given application.